--- title: "Alnor HRU-PremAIR" description: "Alnor HRU-PremAIR heat recovery ventilation unit with Modbus RTU control via BRDG-02R13 communication module." url: "https://taphome.com/en/compatibility/alnor-hru-premair/" language: en lastmod: 2026-03-21 generator: hugo ai: topics: ["modbus-rtu","air-recovery","rs485","heat-recovery","ventilation","humidity"] questions: ["How to integrate Alnor HRU-PremAIR with TapHome?","What does the Alnor HRU-PremAIR TapHome template control?","How to connect Alnor HRU-PremAIR via RS-485 to TapHome?","How to pair the BRDG-02R13 Modbus communication module?","What is the default Modbus slave address for Alnor HRU-PremAIR?","How to monitor indoor humidity with Alnor HRU-PremAIR and TapHome?"] --- # Alnor HRU-PremAIR Communication: Modbus RTU - [Alnor Official Website](https://www.alnor.com.pl) The Alnor HRU-PremAIR is a heat recovery ventilation unit that communicates with TapHome via Modbus RTU over RS-485. The connection requires the **BRDG-02R13** communication module, which plugs into the VMD control board (VMD-02RPS54, VMD-02RPS66 or VMD-02RPS78) inside the recuperator. The template covers ventilation speed control, four temperature sensors (indoor, outdoor, supply, exhaust), bypass monitoring and control, pre-heater status and setpoint, indoor humidity, and fault reporting. The same Modbus protocol applies to HRU-MinistAIR, HRU-SlimAIR and HRU-FlatAIR series units. ## Hardware connection ### RS-485 wiring Connect the BRDG-02R13 module to the TapHome Core RS-485 bus using a twisted pair cable. Multiple devices can share the same RS-485 bus — ensure each device has a unique Slave ID. If the bus line is long or communication problems occur, install a **120 Ohm termination resistor** on both ends of the line as shown in the diagram below. ![Alnor HRQ-Modbus RS-485 termination resistor mounting diagram](https://taphome.com/images/compatibility/alnor-hru-premair/wiring-diagram-p006_hu_5c68d4096c155b70.jpg) > [!WARNING] > **RS-485 termination** — For long cable runs or buses with multiple devices, mount 120 Ohm resistors at both ends of the RS-485 line. TapHome Core has a built-in termination resistor on its BUS terminals, so only the far end of the line needs an external resistor. ### Technical specifications - **Communication module:** BRDG-02R13 (plugs into VMD control board) - **Protocol:** Modbus RTU Slave - **Physical layer:** RS-485 - **Baud rate:** 19200 (default) - **Parity:** Even - **Data bits:** 8 - **Stop bit:** 1 - **Default Slave ID:** 2 - **Modbus functions:** 03 (Read Holding Registers), 16 (Write Multiple Registers) ## Configuration ### Pairing the BRDG-02R13 module Before the communication module can be used, it must be paired with the recuperator. The pairing procedure uses Modbus address **207**: 1. **Power off** the recuperator, then **power it on** — the unit enters binding mode for 10 minutes 2. Write value `0xC84F0001` to registers **43000–43001** 3. Write value `0x0203` to register **43004** 4. Read register **43900** — value should be **2** 5. Read register **43901** — value should be **1** After successful pairing, power off the recuperator and restart it. Data will be read automatically once the fans start up. > [!NOTE] > The pairing procedure requires a Modbus master tool (e.g., Modbus Poll) to write the pairing registers. After pairing is complete, TapHome can communicate with the module at the standard address. ### Slave ID and communication parameters The default Slave ID is **2** and the default baud rate is **19200** with **Even parity** and **1 stop bit**. > [!WARNING] > **Slave ID mismatch** — The TapHome XML template defaults to Slave ID **1** during import. The official Alnor manual states the default Slave ID is **2**. When importing the template in TapHome, change the Slave ID parameter to **2** (or to match your configuration). Communication parameters can be changed via the pairing address (207): | Parameter | Register | Default | Options | |-----------|----------|---------|---------| | Slave address | 42001 | 207 (RS-485) | 1–207 | | Baud rate | 42000 | 6 (19200) | 0=300 ... 5=9600, 6=19200, 7=38400 ... 9=115200 | | Parity | 41998 | 2 (Even) | 0=None, 1=Odd, 2=Even | | Stop bits | 41999 | 0 (1 stop bit) | 0=1, 1=2 | ## Device capabilities ### Ventilation speed control **Ventilation Speed** (H:41500) is the primary control device — a multi-value switch with seven modes: - **Off** (0) — ventilation stopped - **Away** (1) — minimum speed for unoccupied rooms - **Low** (2) — speed 1 - **Nominal** (3) — speed 2, standard operation - **High** (4) — speed 3 - **Auto** (5) — automatic speed based on sensor readings - **Boost** (7) — maximum speed for rapid air exchange The read value reflects the BRDG internal state, which may differ from the actual fan value during speed transitions. ### Fan speed monitoring Two read-only sensors show the actual fan output as a percentage: - **Exhaust Fan Speed** (H:41001) — exhaust fan output, reported on a 0–200 scale (divided by 200 to get percentage) - **Inlet Fan Speed** (H:41002) — supply fan output, same 0–200 scale A value of `0xFF` indicates the sensor is not available. ### Temperature monitoring The template provides four temperature sensors, all using LittleEndianFloat across two registers: - **Indoor Temperature** (H:41005) — room temperature measured by the recuperator's indoor sensor; also reads **Indoor Humidity** from H:42001, with error codes above 100% clamped to 0 - **Outdoor Temperature** (H:41007) — outside air temperature - **Supply Temperature** (H:41011) — fresh air temperature after heat exchange, supplied to rooms - **Exhaust Temperature** (H:41009) — air temperature leaving the heat exchanger A value of NaN indicates no temperature available. Values below -273°C indicate a sensor problem. ### Pre-heater control - **Pre-heater** (H:41013) — read-only percentage showing current pre-heater output (0% = off, 100% = maximum) - **Pre-heater Setpoint** (H:41011 read / H:42011 write) — thermostat device that reads the current supply temperature and allows setting the room temperature heating setpoint (0–30°C) ### Bypass monitoring and control - **Bypass Position** (H:41016) — read-only percentage showing the bypass damper position (0% = closed, 100% = open). Values above 120% indicate an error. - **Bypass Auto** (H:41550) — switch showing the bypass automatic mode state. The module-level write script controls bypass operation: when set to ON, writes `0xFF` (auto mode); when set to OFF, writes the manual level value. - **Bypass Speed** — dimmer device for manual bypass speed override (placeholder in current template) ### Fault monitoring **Fault Status** (H:40103) reports the fan health: 0 = fan OK, 1 = fan failure. This appears as a binary contact sensor in TapHome. ### Service diagnostics The module exposes additional service attributes for monitoring: - **RF Communication Status** (H:40101) — 0 = no error, 1 = no communication for 30+ minutes - **Battery Status** (H:40102) — 0xFFFF indicates no battery - **Actual Ventilation Speed** (H:41000) — raw ventilation speed value including override states (11–13 = temporary override, 22 = away, 23 = boost, 24 = auto) - **Error Code** (H:41003) — detailed error code (0 = no fault, 1–8 = specific errors, 254 = binding mode, 255 = identification) - **Override Time Remaining** (H:41004) — minutes remaining for temporary speed override - **Filter Dirty** (H:41014) — 0 = filter OK, 1 = filter needs replacement - **Defrost** (H:41015) — 0 = inactive, 1 = defrost cycle active The module also provides a **Reset Air Filter Timer** service action that writes value 0 to register H:42000 to reset the filter maintenance countdown. ### Additional capabilities The HRU-PremAIR also exposes registers for individual fan speed configuration (supply and exhaust percentages for each speed level), frost protection pre-heater setpoint, room temperature cooling offset, fireplace demand duration, and post heater/cooler settings on the VMD-02RPS66 and VMD-02RPS78 models. The advanced models also support full time schedule programming via registers 49000–49062 with switch points, day-of-week scheduling, and sensor-based auto control (RH, CO2, VOC, temperature). These can be added in a future template update. > [!TIP] > The community **alnor-sdk** Python SDK defines additional registers not in the official manual — supply/exhaust flow in m3/h (41019/41021), filter days remaining (41040), pre-heater availability (41027), and bypass mode status (41050). These may work on newer firmware versions and could be added as custom Modbus devices in TapHome. ## Troubleshooting ### No Modbus communication 1. **Check the Slave ID** — the default is **2**, not 1. Verify the TapHome module is configured with the correct Slave ID 2. Confirm TapHome RS-485 settings: **19200 baud, Even parity, 8 data bits, 1 stop bit** 3. Verify the BRDG-02R13 module is properly paired (see pairing procedure above) 4. Check RS-485 cable connections — ensure A/B polarity is correct 5. For long cable runs, verify 120 Ohm termination resistors are installed ### Communication errors after power cycle After a power cycle, the recuperator enters binding mode for 10 minutes. During this time, normal Modbus communication may not work at the standard address. Wait for the binding mode to expire. ### Humidity reading shows 0% The Indoor Humidity register (H:42001) returns error codes above 100% (0xEF–0xFF) when the sensor is unavailable, shorted, or out of range. The template clamps these error values to 0. Check the physical humidity sensor connection if readings are consistently 0%. ### Filter alarm When the Filter Dirty service attribute shows 1, the air filters need replacement. After replacing the filters, use the **Reset Air Filter Timer** service action in TapHome to clear the alarm and reset the maintenance countdown. ## Available devices Alnor HRU-PremAIR Module Exhaust Fan Speed Variable Read-only Exhaust fan output as percentage — 0% stopped, 100% maximum speed Register: H:41001 Int16 Unit: % numeric Inlet Fan Speed Variable Read-only Supply fan output as percentage — 0% stopped, 100% maximum speed Register: H:41002 Int16 Unit: % numeric Bypass Auto Switch Read-only Bypass automatic mode — ON enables automatic bypass control, OFF allows manual override Register: H:41550 Int16 boolean-threshold Values / States: ON · OFF Bypass Position Variable Read-only Bypass damper position — 0% closed, 100% open; values above 120% indicate error Register: H:41016 Int16 Unit: % numeric Bypass Speed Dimmer Exhaust Temperature Temperature Sensor Read-only Register: H:41009 LittleEndianFloat Unit: °C numeric Fault Status Reed Contact Read-only Fan health indicator — 0 means OK, 1 means fan failure Register: H:40103 Bool Indoor Temperature Temperature Sensor Read-only Register: H:41005 LittleEndianFloat Unit: °C numeric Outdoor Temperature Temperature Sensor Read-only Register: H:41007 LittleEndianFloat Unit: °C numeric Pre-heater Variable Read-only Pre-heater output level — 0% off, 100% maximum heating Register: H:41013 Int16 Unit: % numeric Pre-heater Setpoint Thermostat Room temperature heating thermostat — reads supply temperature, writes heating setpoint (0–30°C) Register: H:41011 → H:42011 LittleEndianFloat Unit: °C numeric Supply Temperature Temperature Sensor Read-only Fresh air temperature after heat exchange, supplied to rooms Register: H:41011 LittleEndianFloat Unit: °C numeric Ventilation Speed Multi-value Switch Ventilation speed selector — Off, Away, Low, Nominal, High, Auto, Boost Register: H:41500 Int16 multi-value Values / States: Off · Away · Low · Nominal · High · Auto · Boost **Connection:** Modbus RTU • 19200 baud• 8E1 • Slave ID: $\[SlaveId] Possible improvements (23) - H:42002 Standby Speed Supply — RW, 0–40%, fan standby speed setting - H:42003 Low Speed Supply — RW, 0–80%, low speed supply fan setting - H:42004 Low Speed Exhaust — RW, 0–80%, low speed exhaust fan setting - H:42005 Medium Speed Supply — RW, 0–100%, medium speed supply fan setting - H:42006 Medium Speed Exhaust — RW, 10–100%, medium speed exhaust fan setting - H:42007 High Speed Supply — RW, 0–100%, high speed supply fan setting - H:42008 High Speed Exhaust — RW, 10–100%, high speed exhaust fan setting - H:42009 Frost Protection Pre-heater Setpoint — RW, FLOAT, -20–50°C, frost protection threshold - H:42013 Room Temperature Heating Setpoint (duplicate) — RW, FLOAT, 0–30°C, same as 42011 but second instance - H:42015 Room Temperature Cooling Offset — RW, FLOAT, 1–10 K, cooling hysteresis - H:42017 Post Heater/Cooler Supply Heating Setpoint — RW, SINT8, -20–50°C, VMD-02RPS66/78 only - H:42018 Post Heater/Cooler Supply Cooling Offset — RW, UINT8, 0–10 K, VMD-02RPS66/78 only - H:42019 Maximum Constant Pressure — RW, UINT16, 0–500 Pa, VMD-02RPS66/78 only - H:42020 Fireplace Demand Duration — RW, UINT16, 0–60000 sec - H:41501 Override Time Speed 1 — W, UINT8, max 18h, triggers temporary speed 1 override - H:41502 Override Time Speed 2 — W, UINT16, max 18h, triggers temporary speed 2 override - H:41503 Override Time Speed 3 — W, UINT16, max 18h, triggers temporary speed 3 override - H:49000–49062 Time Schedule Registers — Full time schedule programming — VMD-02RPS66/78 only; includes switch points, day-of-week, modes - H:41019 Supply Fan Speed (m3/h) — Flow rate in m3/h — SDK-only register, may require newer firmware - H:41021 Exhaust Fan Speed (m3/h) — Flow rate in m3/h — SDK-only register, may require newer firmware - H:41027 Preheater Available — Pre-heater presence flag — SDK-only register - H:41040 Air Filter Days Remaining — Filter maintenance countdown — SDK-only register - H:41050 Bypass Mode Status — Current bypass mode — SDK-only register ## Sources - Alnor HRQ-Modbus User's Manual — Modbus Communication Protocol for HRU-PremAIR [www.alnor.com.pl](https://www.alnor.com.pl/assets/files/instrukcje-obslugi/Instrukcja-modbus-PremAIR-PL-EN.pdf) 2026-03-21 [PDF](https://taphome.com/compatibility/devices/alnor-hru-premair/manufacturer/modbus-manual.pdf) - alnor-sdk — Python SDK for Alnor Ventilation Devices [github.com](https://github.com/nashant/alnor-sdk) 2026-03-21 ## Related Documentation - [Modbus Integration](https://taphome.com/en/compatibility/modbus-guide/) - [Modbus](https://taphome.com/en/docs/integration/modbus/) - [Simple configuration using templates](https://taphome.com/en/docs/integration/modbus/templates/) - [Modbus scripts and prefetch](https://taphome.com/en/docs/script/modbus-scripts/) - [Modbus functions](https://taphome.com/en/docs/script/modbus/) - [Modbus data types](https://taphome.com/en/docs/script/modbus-data-types/)